[R-390] PTO SUCCESS!!

[Bill Smith]

Congratulations!  Have been following your story with great interest.  Good
work.

73 de Bill, AB6MT
billsmith@ispwest.com

----- Original Message -----
From: Phil Atchley
To: r-390@mailman.qth.net
Sent: Tuesday, July 08, 2003 7:55 PM
Subject: [R-390] PTO SUCCESS!!


Hi.
Well, I finally met with success in getting a PTO set up for this '67 EAC.
If you recall this Cosmos PTO had a linearity ring with a crushed
"footbridge".  It's not perfect, but it is much, much better than when it
arrived here.  Smooth tuning and no minor frequency jumps when tuning
either!

Well, the PTO that arrived in the mail was also a Cosmos.  It worked but had
a number of "issues" with it also.  Notably the damaged Coax cable, the
damaged slug screw for the output transformer etc.  BUT, the one thing it
did have was a good linearity ring.  So, I decided to rebuilt the one that
came with the receiver as it was otherwise in pretty nice condition.

First order of the day was to tear both PTO's all the way down to the inner
sanctum where the linearizing hardware resides.  I then swapped the
linearizing rings, backed all the linearizing screws counterclockwise and
then one turn clockwise.

Reassembling the unit it took about 4 tries before I got the disk in the
right position so that I had screws at both ends of the tuning range.  I had
previously marked the tuning slug position for 3455KHz to make it easier.  I
quickly discovered that I could pull the assembly far enough apart to
reposition the disk without having to take the lead screw all the way out of
the tuning slug.  This helps keep things in position.

While reassembling the unit one other problem reared it's ugly head.  I had
previously mentioned this PTO was not "virgin".  Somebody had worked on the
coil tap for the main tuning coil.  In the process of taking the wire off
the feedthru this same wire pulled loose from the coil, breaking the winding
in two (previously repaired).  So, my fix was to solder a heavier piece of
hookup wire to the feedthru, carefully position this over the two ends of
the broken wire and solder them.  Some clear fingernail polish then secured
the fine wires to the coil form and the hookup wire.  I was very careful how
I positioned this wire, even so I was afraid that it might affect the tuning
range of the coil.  However, I was pleasantly surprised that upon
re-assembly the PTO tuned just fine, the 3455 position being just about
where it was when I removed it (A little difference but I attribute that to
the fact that I backed the linearizing screws out).

You might ask, if I had two PTO's here and was using one for parts, why
didn't I rob the tuning coil out of the parts unit?  Good question!  The
answer is simple.  While both were Cosmos units there were significant
differences in the two units, particularly around the tuning coil.  I'm sure
the coils were electrically the same, however the hook-ups were somewhat
different, the older unit having three feedthru wires to the oscillator, two
of which were from the coil.  The other unit (one I used) had only two
feedthru wires.

All the above was THE EASY PART!!  It took me a good 10-12 hours of work to
set the end points AND all the linearizing screws.  I had no test jig so I
did it in the set, using the Veeder Root counter and lifting PTO out of the
set for each adjustment.  I quickly found out that if I left the back
bracket on but not screwed to the chassis and left the front screws
unscrewed from the chassis I could hold it in position, tune up to the next
point, lift PTO out and tweak it and re-insert the PTO without knocking the
PTO shaft out of position (I have a fine touch ;-) .

It also took several trips through the routine as I found that the first
setting I did for end points was not optimum for having sufficient range on
all the linearizing screws.  The final results are that I have a couple
screws that are backed all the way out, MOST in the mid-range and a couple
in as far as I could go without getting any binding on the PTO tuning.
Where there was any problem there I backed them out a little more than the
optimum point as I figured a couple hundred Hz non-linearity was better than
getting the screws too tight.

No, this is NOT a PERFECT PTO, worst case non-linearity is at 025 KHz where
it actually reads 025.7 on the counter (000 and 050.1 on 25KHz points either
side).  AVERAGE non-linearity is probably better than 300 Hz, this with the
end points at 000 and +000 being dead on the money.  I think some of the
non-linearity may be due to the repairs that have had to be made to the
tuning coil etc. That and if I had a test jig where I could EASILY adjust
the critter it may have made a difference.  Not having a frequency counter I
used my Yaesu VR-5000 in LSB mode to Zero Beat the PTO when the Yaesu
receiver was tuned to the desired frequency.

However, I DO feel pretty good about rescuing what was otherwise a "Sows
Ear" and which was useful only for parts!   BESIDES, THEY DON'T MAKE PTO'S
LIKE THEY USED TO 8^)

NOTES:
DIFFERENCES BETWEEN THE TWO COSMOS PTO'S (#1 came in my receiver).  It
appears that unit #1 is a much newer PTO than unit #2.
1.  PTO#1 had two feedthru wires from coil to oscillator.
    PTO#2 had three feedthru wires from coil to oscillator.
2.  PTO#1 had new style coax with clear jacket, good condition.
    PTO#2 had old green coax with cover and shield broken at body.
3.  PTO#1 had slotted linearizing screw shafts for screwdriver.
    PTO#2 had some sort of hex or fluted linearizing screw shafts.
4.  PTO#1 Disk had a number of missing linearizing screws.
    PTO#2 Disk had linearizing screws in all holes.
5.  PTO#1 Heater wires entered through front of PTO unit.
    PTO#2 Heater wires entered through side of outer can.

73 de Phil, KO6BB

****************************************************
*  DXing THE WORLD WITH THE FOLLOWING EQUIPMENT.   *
*  RECEIVERS:                                      *
*    '67 EAC R-390/URR Surplus Receiver with a     *
*            HAMMARLUND HC-10 Sideband adapter.    *
*    YAESU VR-5000 Wideband,  REALISTIC DX-392.    *
*    Home built Longwave "Hybrid" CW receiver.     *
*    Others which pass thru or are waiting repair. *
*  ANTENNAS:                                       *
*    Coil Loaded 18.5 Meter Long Sloper.           *
*    Roof mounted Hustler 6BTV 6 band Vertical.    *
*    Scantenna Scanner antenna at 7 Meters high.   *
*  LOCATION: Merced, Central California.           *
****************************************************




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